Selective affinity material, preparation thereof by molecular imprinting, and use of the same

ABSTRACT

A selective adsorption material, especially suitable for adsorption of biological macromolecules, is described. The, adsorption material comprises a matrix with immobilised ligands, localised to selectively adsorb a predetermined molecule. A process for preparing a selective adsorption material, especially suitable for adsorption of biological macromolecules, is also described. The process is characterised in that a print molecule having at least two separate binding sites is bonded to the corresponding, at least two immobilisable ligands, the ligands are immobilised, and subsequently the print molecule is removed. The selective adsorption material can be used for purification or analysis, especially of biological macromolecules.

[0001] The invention relates to a selective adsorption material, especially suitable for adsorption of biological macromolecules, a process for preparing this selective adsorption material, and the use thereof for purification and analysis, especially of biological macromolecules.

[0002] It Is known to prepare homogeneous gels while using the so-called molecular imprinting technique by making imprints of dyes (R. Arshady, K. Mosbach; Makromol. Chemie, 182 (1981) 687) and amino acid derivatives (L. Andersson, B. Sellergren, K. Mosbach, Tetrahedron Lett. 25 (1984) 5211). Merely non-covalent bonding between a “print molecule” and monomers is used. After polymerisation of the monomers and removal of the print molecule, a selective polymer is obtained, based on binding groups correctly immobilised in space and present in cavities which have the shape of a mould of the print molecule. A summary of this technique is given by B. Ekberg, K. Mosbach, in Trends Biotechnol., 7 (1989) 92.

[0003] It is known to make imprints of carbohydrate derivatives substituted with covalently, but reversibly bonded vinylphenyl boric acid groups, so-called boronate esters, which after polymerisation have permitted hydrolysis and binding of a new print molecule (G. Wulff, ACS Symp. Series, 308 (1986) 186). Decisive of the selectivity of the thus prepared polymers are correctly positioned binding boronate groups and a well-shaped cavity. The drawback of this system is that a complicated chemical synthesis is necessary.

[0004] Prearranged boronate groups have also been used for Faking imprints of glycoprotein ((Transferrin, M. Glad, O. Norrlöw, B. Sellergren, N. Siegbahn, K. Mosbach, J. Chromatogr., 347 (1985) 11) and bis-nucleotides O. Norrlöw, M. O. Mánsson K. Mosbach. J. Chromatogr., 396 (1987) 374) on silica. In this context, use has been made of a mixture of non-covalently bonding organic silanes and boronate silane, which has been caused to interact with a print molecule before polymerisation on the surface. The effect of recognition seems mainly to depend on the fact that the boronate groups are correctly spaced from each other to be able to interact effectively with the print molecules. Transferrin has a total of four silica acid groups and bis-NAD has four riboses which form boronate esters.

[0005] It is also known to use, in affinity chromatography methods, adsorption material having specific ligands, but these are randomly localised on the sorbent and may therefore yield poor selectivity. Furthermore, there will be a large number of unused ligands, which is uneconomical from the industrial point of view.

[0006] Immobilised phenyl boric acid has been used to separate carbohydrate derivatives (H. L. Weith, J. L. Wiebers, P. T. Gilham, Biochemistry, 91 (1970) 4) and also to separate glycosylised hemoglobin and other glycoproteins (P. D. G. Dean, P. J. Brown, V. Bouriotis, U.S. Pat. No. 4,269,605 (1981).

[0007] For purification and analysis, especially of biological macromolecules, selectivity is most important. It is frequently necessary to distinguish a single component in a mixture of, maybe, several thousand components. The known adsorption materials are in most cases not sufficiently selective and cause non-specific binding, which may completely destroy the result of an analysis.

[0008] Modern biotechnical production and analysis as well as a large amount of medical diagnostics are based on selective binding. The methods known so far are also for these purposes not sufficiently selective and/or sufficiently simple to be economically useful on an industrial scale. Therefore there is a need of an adsorption material having very high selectivity and low non-specific binding, which may be prepared on a large scale and at low cost.

[0009] According to the invention, a selective adsorption material is provided, which is especially suitable for adsorption of biological macromolecules, and which is characterised In that it comprises immobilised ligands which have been localised to selectively adsorb a predetermined molecule by their first being bound to a print molecule which has then been removed after the immobilisation of the ligand.

[0010] The invention also comprises a process for preparing a selective adsorption material, especially suitable for adsorption of biological macromolecules, characterised in that a print molecule having at least two separate binding sites is bonded to the corresponding, at least two immobilisable ligands, that the ligands are immobilised, and that subsequently the print molecule is removed.

[0011] Finally the invention relates to the use of the selective adsorption material for purification or analysis, especially of biological macromolecules.

[0012] After prebonding to the print molecule and the subsequent immobilisation, the binding groups (ligands) will be bonded preferably to the surface of a matrix. The correct localisation of ligands on two dimensions results in increased selectivity by the print molecule having at least two separate binding sites. The corresponding, at least two immobilised ligands will thus be correctly spaced apart. This results in optimal binding of the target molecule in the subsequent adsorption.

[0013] As is evident from that stated above, the invention thus relates to a form of directed immobilisation of affinity ligands or other (chemical) ligands. This directed immobilisation is achieved by means of a prebinding method. The advantage as compared to randomly immobilised binding groups is that the print molecule is bonded more effectively and with greater selectivity. At the same time, all ligands may be utilised, thereby avoiding an excess thereof, which otherwise may easily result in non-specific bonding which in turn results in a lower yield.

[0014] Ligands which are useful for the invention should carry groups that can be bonded to a print molecule, and groups which can be used for immobilisation of the ligands. One type of suitable ligands is monomers which can be immobilised by polymerisation. Examples of groups that can be bonded to a print molecule are given In Table 1. TABLE 1 Group binding to print Binding group on print molecule on ligand/monomer molecule Imidazole-metal Histidine, tryptophane, thiol Iminodiacetic acid-metal ″ Carboxyl Amine Amine Carboxyl Carboxyl Carboxyl, amide (hydrogen bonding) Boronate Carbohydrate, diol Thiol Thiol Aldehyde Amine

[0015] Boronate, thiol and aldehyde are bonded covalently, whereas the other groups are bonded non-covalently to the print molecule.

[0016] Among groups that may be used for immobilisation, mention can be made of silanes which bind silanol and hydroxyl groups, and vinyl, acryl and methacryl which polymerise an a matrix.

[0017] Other ligands/monomers that may be used are:

[0018] Acryloyhistamine; H. Morawetz, W. R. Song, JACS, 88 (1966) 571.

[0019] Boronate silane: M. Glad, O. Norrlöw, B. Sellergren, N. Siegbahn, K. Mosbach, J. Chromatogr., 347 (1985) 11.

[0020] IDA-silane: A. Figueroa, C. Corradini, B. Felbush, B. L. Karger, P. Chromatogr., 371 (1986) 335.

[0021] Moreover, different types of ligands may be used simultaneously in one preparation. For example, use can be made of both boronate binding and metal interaction on the same print molecule if this is e.g. a glycoproten with surface-bound histidines.

[0022] As print molecule (imprinting molecule) for prearrangement of the ligands, the invention preferably uses biological macromolecules, e.g. enzymes, antibodies, glycoproteins or other proteins, nucleic acids, polysaccharides. The molecular imprinting is preferably carried out in aqueous media which are the normal surroundings of these molecules. It has also become apparent that larger or smaller amounts of organic solvents which are miscible with water, such as DMF, DMSO, formamide (M. St{dot over (a)}hl, M. O. M{dot over (a)}nsson, K. Mosbach, Biotechn. Lett., 12 (1990) 161; N. Chang, S. J. Hen, A. M. Klibanov, BBRC, 176 (1991) 1462), may be added. In some cases, also pure DMSO can be used, in which protein and a monomer mixture (the ligands) are dissolved. A polymerised product is obtained, having a sufficient amount of correctly positioned, binding groups to provide a certain selectivity.

[0023] Matrix materials which are useful according to the invention must contain surface-bound reactive groups which can react with and covalently bind prearranged ligands. The matrices may be solid or in the form of gels and comprise particles, chips, electrodes, gel etc. Suitable matrix materials are silica (particles, chips etc.), glass (particles, electrodes etc.), biological polymers (agarose, dextran, gelatin etc.) and synthetic polymers (polyvinyl alcohol, TRIM (P. Reinholdsson, T. Hargitai, B. Törnell, R. Isaksson, Angew. Macromol. Chem., 1991, in press) etc.) When the matrix consists of a particulate solid phase, the surface is to be found both on the outside of the particles and on the surface of the pores thereof. In most cases, the latter surface is many times larger than the former.

[0024] Reactive groups on the matrix material can be acrylate, methacrylate. vinyl, hydroxyl or silanol.

[0025] If the matrix material contains no suitable reactive groups, it may be derivatised in advance with suitable groups, such as methacryl groups, before immobilising the ligands on the matrix.

[0026] The difference between a prior art adsorption material and the invention is schematically shown in the accompanying drawing in which:

[0027]FIG. 1 is a schematic sketch of a prior art sorbent with randomly positioned, binding groups, e.g. boronate, immobilised metal; and

[0028]FIG. 2 shows a sorbent according to the invention, with specifically localised, binding groups.

[0029] The invention will now be described in more detail by means of the following, non-restrictive Example.

EXAMPLE

[0030] Methcrylate Silica

[0031] 3-methacryloyloxypropyltrimethoxysilane (2.0 g, 8.1 mmol, Fluka) was mixed with 100 ml of water and dissolved during powerful stirring by means of a magnetic stirrer at 22° C. for 4 h. Porous silica (5.0 g, “Lichrospher Si 300”, Merck) was suspended in 20 ml of water and treated with vacuum and ultrasonics, thereby producing pores free from air. Subsequently, the silane solution was added, and the silanisation was allowed to proceed for 4 h at 60° C. in a round-bottomed flask placed In a water bath and fitted with a “Teflon®”-coated blade mixer. The derivatised silica was washed on a glass filter with water and methanol and then air-dried on the filter.

[0032] Titration with bromine water (according to Glad et al, J. Chromatogr., 347 (1985) 11) yielded 335 μmol of methacrylate groups per g of silica product. A carbon analysis yielded 620 μmol of silane per g of silica product, which indicates that more than half of the groups are still reactive to subsequent immobilisation.

[0033] Preparation

[0034] Mixtures according to the Table below with RNase B and STI (Soybean trypsine inhibitor), respectively, as print molecule. mg μmol Methacrylate-silica 800 268 Vinyl imidazole¹⁾ 0.39 4.14 Acrylphenyl boric acid 1.59 8.32 Acrylamide 100 1410 PDA (piperazine diacrylamide) 50 257 TEMED 5 ZnCl₂ 0.64 4.70 Water/DMF (7/3, w/w) 2.5 ml Ammonium persulphate alt. A) RNase B (molecular 10 0.73 weight 14700) alt. B) STI (molecular 10 0.53 weight 20100)

[0035] After mixing the respective print molecule with all the other ingredients in a total of 2.5 ml of water/DMF, the samples were cooled, and then N₂ gas was conducted through the mixture. After about 30 s, the mixture began to solidify. The preparation was allowed to stand for 1 h, and subsequently the substituted silica particles were washed on a glass filter with water/DMF. Small polymer particles were removed by sedimentation, and the remaining particles were packed in steel columns (5×0.5 cm). When injecting RNase B on preparation A, the elution was delayed as compared with preparation B.

[0036] As an alternative to vinyl imidazole, vinyl benzyl iminodiacetic acid can be used (L. R. Morris, R. A. Mock, C. A. Marshall, J. H. Howe, JACS, 81 (1959) 377). These bind metal ions, e g. Zn²⁺, Cu²⁺, which have been used for a long time in so-called immobilised metal affinity chromatography (J. Porath, J. Carlsson, I. Olsson, G. Belfrage, Nature. 258 (1975) 598). 

1. Selective adsorption material suitable for adsorption of biological macromolecules, characterised in that it comprises at least two immobilised ligands which have been localised to selectively adsorb a predetermined molecule by their first being bound to at least two separate binding sites on a print molecule which has then been removed after the immobilisation of the ligands, whereby the ligands have been bound to the print molecule via one or more of the groups imidazole-metal, iminodiacetic acid-metal, carboxyl, amine, boronate, thiol and aldehyde on the ligands.
 2. Adsorption material as claimed in claim 1, characterised in that the ligands have been bound to the print molecule via the groups imidazole-metal and/or iminodiacetic acid-metal on the ligands.
 3. Adsorption material as claimed in claim 1 or 2, characterised in that the ligands are polymerisable monomers which have been immobilised by polymerisation.
 4. Adsorption material as claimed in any one of the preceding claims, characterised in that the ligands are immobilised by covalent bonding to a matrix having surface-bound groups which are reactive with the ligands.
 5. Adsorption material as claimed in claim 1 or 2, characterised in that the ligands are immobilised in a polymer network which is polymerised or bonded to a matrix.
 6. Adsorption material as claimed in claim 4 or 5, characterised in that the matrix is selected among silica, glass, biological polymers, synthetic polymers and mixtures thereof.
 7. Adsorption material as claimed in one or more of the preceding claims, characterised in that the ligands are chosen among at least two different types of ligands.
 8. Process for preparing a selective adsorption material, especially suitable for adsorption of biological macromolecules, characterised in that a print molecule having at least two separate binding sites is bonded to the corresponding, at least two immobilisable ligands via one or more of the groups imidazole-metal, iminodiacetic acid-metal, carboxyl, amine, boronate, thiol and aldehyde on the ligands, whereupon the ligands are immobilised, and subsequently the print molecule is removed.
 9. Process as claimed in claim 8, characterised in that the ligands are bound to the print molecule via the groups imidazole-metal and/or iminodiacetic acid-metal on the ligands.
 10. Process as claimed in claim 8 or 9, characterised in that the ligands are polymerisable monomers and are immobilised by direct polymerisation.
 11. Process as claimed in claim 8 or 9, characterised in that the immobilisation of the ligands is effected by covalent bonding to a matrix having surface-bound groups which are reactive with the ligands.
 12. Process as claimed in claim 11, characterised in that the matrix is, by prederivatisation, provided with groups which can react with the ligands.
 13. Process as claimed in claim 8 or 9, characterised in that the ligands are immobilised by binding in a polymer network which is polymerised or bonded to a matrix.
 14. Process as claimed in any one of claims 11-13, characterised in that the matrix is selected among silica, glass, biological polymers, synthetic polymers and mixtures thereof.
 15. Process according to any one of claims 8-14, characterised in that the ligands are chosen among at least two different types of ligands
 16. Use of the selective adsorption material as claimed in one or more of claims 1-7, for purification or analysis, especially of biological macromolecules. 